The present invention relates to an electrical current sensor comprising a coil made of a wound electrical conductor, and a method of manufacturing the current sensor. The invention relates in particular to a current sensor with a coil formed of self-supporting windings made of an electrical conductor with a cross-sectional area greater than 0.3 mm2.
In electrical current sensing applications, it is well-known to provide a current sensor comprising a coil with one or more turns through which a primary current to be measured flows, the magnetic field generated by the primary current flowing through the coil being detected and used as a measure of the primary current.
The number of windings of a coil affects the amplitude of the magnetic field generated or picked up by the coil and it is thus important to ensure good electrical insulation between windings of a coil. In current sensing applications the dimensional accuracy of the coil may also be important to ensure accurate and efficient measurement of the parameter to be measured.
One common technique for ensuring insulation between windings of a coil is to coat the wire conductor forming the coil with a dielectric outer coating layer. Extremities of the conductor forming the coil need to be electrically interconnected to an electrical circuit which thus requires removal of insulation from the connection ends of the conductor. This is difficult and costly to implement in an automated manufacturing process, particularly for connection ends that require a relatively large connection surface or that are configured for surface mount solder connection to circuit boards.
For current sensor coils made of only a few windings for example from one to ten windings, made of a relatively thick self-supporting conductor, it is known to form the windings of the coil from a non-coated conducting bar or wire such that the winding forms a helical shape where the windings of the coil are separated by an air gap. The helical coil portion is then overmolded with an insulating material, such that insulating material fills the air gap between the windings. Alternatively, in certain applications the helical coil winding is simply lodged in a housing whereby the electrical insulation between windings of the coil is provided simply by the air gap which is intended to be maintained by the rigidity of the conductor wire or bar forming the coil. Once the helical windings of the coil have been formed, the air gap between the windings, or more generally the geometry of the windings, may be altered during transport or storage of the coils or during the overmolding or assembly process such that the distance separating adjacent windings is insufficient to ensure adequate electrical insulation for the desired accuracy and performance of the coil during its intended use. The care required for handling of the coil windings once formed also increases manufacturing costs.